I think it's hinge I'm not so sure though :/
In a study, the independent variable is the thing that you change to see how the change produces different results. In this study, the independent variable would be the use of nicotine.
Answer:
In general, children and teens need about 6 to 8 cups of water a day. They should also eat lots of fresh fruits and veggies, which are full of water. During play or exercise, a good goal is to drink a half cup to 2 cups of water every 15 to 20 minutes.
Explanation:
